This invention relates to control of an automotive vehicle equipped with an electronic control unit for controlling devices mounted on the vehicle.
The appearance of electronically controlled vehicles controlled by an electronic control unit (commonly referred to as an "ECU") comprising a microcomputer has increased in recent years. In addition to control of the rotational speed of the internal combustion engine, control of gear changeover in a transmission and control of a clutch, these vehicles also have various accessories controlled by the electronic control unit. Based on signals from various sensors provided on a variety of actuators, which drive devices to be controlled, the electronic control unit calculates control variables for the various actuators that are controlled and then outputs the corresponding signals to these actuators to control the operation of each device. Such a system is illustrated in Japanese Patent Application No. 60-217471 filed by the present applicant. This electronically controlled vehicle not only includes an electronic control unit (main electronic control unit) for controlling various actuators that is also equipped with emergency actuators for back-up purposes in the event that any actuator or the main control unit itself develops an abnormality such as breakage of a wire or short circuit, and an emergency electronic control unit for controlling the emergency actuators. If the main electronic control unit should happen to malfunction, the system is switched over to the emergency electronic control unit to assure that the vehicle will continue to travel safely.
In this electronically controlled vehicle, however, the emergency electronic control unit is not used when the various actuators are operating normally, so that it is impossible for the driver to know whether the emergency electronic control unit has developed an abnormality.
Since the emergency electronic control unit must operate without failure if the main electronic control unit malfunctions, it is necessary that some form of warning means be provided to inform the driver of whether the emergency electronic control unit is operating abnormally, even when the vehicle is operating in the normal traveling mode, i.e. under the control of the main electronic control unit.